I've seen both sides shimmed, I guess not at once but some install the shim on the pass.side and I've also seen it on the driver side or clutch side.
Just wanna know where local tranny builders put them.

For the sealed roller bearings: the shim goes in the passenger side axle hole of the transmission. This allows you to make sure the diff is totally seated in the clutch housing side (aka driver side), and measure the clearance thru the passenger side axle hole.
Service manual states the clearance should be 0 - 0.1 mm